Since diesel engines come into being, they have been widely applied in various propulsion installation, ships and vehicles due to their advantages such as excellent dynamic performance, cost-effectiveness and durability. Compared with gasoline engines, diesel engines have many advantages: reduced exhaust gas emission, better acceleration performance at a lower vehicle speed, lower average fuel consumption, and more driving fun. However, as compared with the gasoline engine with the same power, the diesel engine emits particulates and oxynitride which are two most major pollutants in the exhaust gas.
At present, a technology for reducing vehicle exhaust gas emission to meet an emission standard usually employs an exhaust gas post-treatment manner to reduce the emission of pollutants. Amongst others, urea selective catalytic reduction (SCR) method is a method which is of the most practical significance and it may effectively reduce oxynitride in the exhaust gas of the engine.
In a SCR urea metering injection system of an existing diesel engine (hereinafter referred to as a urea injection system), a PID type control policy is employed for controlling urea pressure, which requires massive calibration work. Besides, based on the existing PID control policy and in some operation conditions of an engine, there would a large deviation between an actual value and the target value of the urea pressure, which causes a relatively larger deviation between an actual injection amount of urea and a target urea injection amount in the urea injection system, which therefore directly affects conversion rate of oxynitride in the engine post-treatment SCR system.
Based on the above reasons, it is of crucial importance to develop advanced urea pressure control policy of the urea injection system to improve the engine performance and reduce the calibration work. To this end, there is a need in the art to improve the control technology for the urea injection system.